Draft gear assemblies which utilize friction-type clutch mechanisms to absorb heat energy generated during service have been in widespread use on railway cars for several years prior to the present invention, as is generally well known in the railway art. These draft gear assemblies are disposed within an elongated opening located in the center sill member of the railway car along the longitudinal axis thereof and behind the shank, or innermost end, of the railway car's coupling mechanism. In this position, these friction clutch type draft gear assemblies will absorb at least a relatively large portion of both the buff and draft forces generated during service. Such buff and draft forces encountered by such railway car are usually being applied in an alternating manner to the center sill member during normal car operation on the track.
A representative teaching of such prior art type friction clutch draft gear assemblies can be found, for example, in U.S. Pat. Nos. 2,916,163; 3,178,036; 3,447,693; 4,576,295; 4,645,187 and 4,735,328. Most, if not all, of these prior art type draft gear assemblies either have been or still are being utilized in the railway industry prior to the development of the present invention. Furthermore, except for U.S. Pat. Nos. 4,576,295 and 4,735,328, each of the remaining above-identified patents is owned by the assignee of the present invention. The teachings of each of the above-referenced patents are incorporated herein by reference thereto.
It is quite well recognized, by those persons who are skilled in the friction clutch type draft gear assembly design art, that these draft gear assemblies must be provided with the capability of maintaining at least a certain minimum shock absorbing capacity both during making up a train consist and in-track service. Such minimum capacity has been specified by the Association of American Railroads (AAR). For example, friction clutch type draft gear assemblies have a specified absolute minimum capacity rating of at least 36,000 foot pounds. Any draft gear assembly with a capacity rating which is determined to be below 36,000 pounds will not receive approval from the AAR for service on any railroad car which may be used in interchange.
It is, likewise, important to note that the heat energy absorbing action of the friction clutch mechanism must enable this minimum capacity rating to be readily achieved without exceeding a specified maximum 500,000 pound reaction force, or pressure, being exerted on the center sill member of the railway car during both such make-up and operation of such train consist. It has been found that such maximum reaction pressure is required to enable these high energy shocks to be readily absorbed without upsetting the end of the coupling member shank and/or damaging other critical car components and/or the lading that is being transported by such railway cars.
In order for the manufacturers of such friction clutch type draft gear assemblies to meet the requirements of the railroad industry, with the ever increasing load carrying capacity of their modern day railroad cars, it has become of extreme importance to enhance the overall rated capacity of the friction-type draft gear assemblies as much as possible. This higher capacity rating being found necessary in order to minimize any damage to such cars and/or the lading due to the increased forces being exerted on the center sill member of the cars by the heavier loads such cars are now carrying.
U.S. Pat. No. 5,590,797, owned by the assignee of the present invention and hereby incorporated by reference thereto, relates to a friction clutch mechanism for a high capacity draft gear assembly having a higher capacity rating as discussed above. The friction clutch mechanism in this patent improves upon the prior friction clutch mechanisms by modifying the wedge shoe members. Specifically, in the (′797) patent, the wedge shoe members have a Brinell Hardness of between 429 and 495 and an upper surface which is tapered from a point disposed inwardly from a tapered outer surface inwardly toward and at an acute angle relative to a longitudinal axis of the friction clutch mechanism at an angle of between 46.5° and 48.5°. The ('797) patent also teaches that it is advantageous to include brass inserts in various plate components of the friction clutch mechanism to provide a requisite amount of lubrication necessary to prevent detrimental sticking of the friction clutch mechanism after closure of the friction clutch draft gear assembly and during a release cycle thereof.
While the above discussed design resulted in an improved friction clutch draft gear assembly than those previously in use, it was determined that this particular design does not satisfy the requirements as defined in AAR Specification M-901-G. It was determined during testing of Super Mark 50's, with rusted friction packs, assembled with H-911 brass inserts, that the units tested had reaction force spikes higher than 500K. This resulted in hammer capacities of less than 36,000 ft/lbs. When tested on the test track, the same super Mark 50 reached the 500K reaction force levels well before the 5-MPH requirement for a G specification draft gear. Thus, a need exists in the art for a draft gear assembly that meets the standards as defined in AAR Specification M-901-G.